1. Field of the Invention
The present invention relates to a drive unit for an electric motor vehicle.
2. Description of the Background Art
In a conventional vehicle, a gasoline engine is generally used to generate a torque, which is transmitted to drive wheels after a change in rotational speed by an automatic transmission or a manual transmission. In the gasoline engine, a mixture of gasoline and air is compressed and combusted to generate energy which is output as torque. Therefore, noise is caused by the combustion, and the exhaust gas which is the product of combustion pollutes the environment.
Therefore, it has been proposed to replace combustion engines with electric motors to prevent generation of the noise and exhaust gas. Electric vehicles are equipped with an electric motor and a battery, and the motor rotates drive wheels. With an electric vehicle there is scarcely any noise and exhaust gas is not generated.
FIG. 15 is a cross section of a prior art drive unit for an electric vehicle.
In FIG. 15, 10 is a drive unit, 11 is a motor, and 12 is a differential unit. The motor 11 is formed of a stator 14 fixed to a drive unit casing 13 and a rotor 15 disposed around the stator 14. A direct current is supplied to a coil 16 of the stator 14 to rotate the rotor 15.
The differential unit 12 has a casing 18 integral with the rotor 15, and the rotation of the rotor 15 is transmitted to the casing 18. The casing 18 carries a pinion shaft 19, which extends through the casing 18 and rotatably carries a plurality of pinion gears 20. The pinion gears 20 engage with left and right side gears 21 and 22, through which the rotation is transmitted to left and right drive shafts 23 and 24, respectively.
In the conventional electric vehicle described above, however, the quantity of electricity which can be stored in the battery is restricted, and thus the travelling distance of the vehicle is short. In the travel of a vehicle equipped with an electric motor, the efficiency changes in accordance with the rotational speed, i.e., the vehicle speed. Therefore, a high drive efficiency may be achieved in a high-speed range, in which case the efficiency is low in the low speed range. Conversely, a high drive efficiency may be achieved in a low-speed range, in which case the efficiency is low in the high speed range.
As noted above, a high efficiency throughout the entire speed range cannot be achieved. Further, in high-speed driving, the travelling distance is significantly reduced, and rapid start and rapid acceleration cannot be achieved.
Therefore, there exists a need for an electric vehicle which can achieve high efficiency throughout the entire speed range
FIG. 16 schematically shows another prior art drive unit for an electric vehicle, FIG. 17 is a cross-section of the same prior art unit, and FIG. 18 is a schematic diagram of same.
In FIG. 16, 29 indicates the electric vehicle, 30 is a drive unit for the electric vehicle 29, 31 is an AC motor, 32 is a battery for supplying the current to the motor 31, and 33 is a transistor inverter for converting the DC current supplied from the battery 32 into AC current. The transistor inverter 33 operates in response to a signal from a control unit 34 to generate the AC current.
A change speed lever or shift lever 35, which is disposed near a driver's seat, is operated to set the transmission at an intended speed range as described later. An accelerator 36 is disposed near the driver's seat and is operated to change the rotational speed of the motor 31 and thereby change the speed of the vehicle.
A rotor phase angle sensor 37 sends an output signal to the control unit 34. Various transmission ranges are selected for transmission 38 responsive to movement of the shift lever 35 to change the rotational speed of the motor 31 at a gear ratio complying with the travelling conditions.
In FIGS. 17 and 18, 30 is a drive unit, 31 is the motor and 38 is the transmission. The motor 31 is formed of a rotor 41 and stators 42 and 43 disposed at opposite sides of the rotor 41. The rotor 41 rotates together with a rotor shaft 44 which is rigidly connected to the rotor 41.
The rotor shaft 44 is connected to an input shaft 45 of the transmission 38, and thus the rotation of the motor 31 is supplied to an input shaft 45. 47 indicates an electromagnetic clutch, 48 is a first reduction gear, and 49 is a second reduction gear. A main shaft 50, which is disposed in parallel with the input shaft 45, carries an one-way clutch 51 and a reverse gear clutch 52. A differential gear 55 transmits the rotation, at a speed reduced by a final drive gear 53, to the left and right drive shafts 56 and 57.
In the electric vehicle 29 described above, the rotation of the motor 31 is transmitted to the transmission 38, which can select the necessary speed range, so that the appropriate speed ranges can be achieved for the respective operational regions of the motor 31, and thus relatively high drive efficiency can be achieved throughout the entire range of the vehicle speed. However, the torque generated by the motor 31 is transmitted through the transmission 38 to the drive wheels. Therefore, there is a loss related to the transmission efficiency of the transmission 38, and thus the overall efficiency is insufficient and, also, a complicated speed change mechanism is required.